Many cars and particularly racing cars are provided with rear torsion bar suspension systems utilizing individual torsion bars for the left and right rear wheels respectively. Generally, the torsion bars are axially aligned extending in directions generally parallel to the rear axes of the rear wheels and spaced ahead of the rear wheels. These bars are surrounded by a torsion bar housing tube fixed to the frame of the car. The inner ends of the torsion bars are secured to the housing tube and their oppositely extending outer ends secured to appropriate rear wheel supporting spring plates respectively. Up and down movement of each rear wheel is opposed by a twisting reaction torque from its associated torsion bar.
After prolonged use, the "stiffness" of the suspension system tends to decrease with the result that the rear wheels may swing through a sufficient up and down amplitude as to hit the frame structure of the car or even simply seat on the frame structure. Under these circumstances, it is necessary to "tighten up" the suspension system to restore the original "stiffness". The process of adjusting the individual torsion bars is quite cumbersome. Normally, the car frame must be jacked up, the rear wheels removed, the normal spring plates extending to the outer ends of the torsion bars removed and the individual torsion bars themselves removed from the housing. A greater initial bias or twisting force is then provided in each of the bars and reverse steps are taken in re-assemblying the suspension system and wheels on the car.
Many times after the foregoing adjustments have been made, it is found that too great a degree of "stiffness" has been provided in the suspension system. It is then again necessary to disassemble all of the various components and effect another adjustment to provide somewhat more resiliency; that is, some of the initial bias twist in the bars is reduced.
While more simple means for adjusting torsion bar suspension systems are known, for those types of automobiles or racing cars wherein the rear suspension torsion bars themselves are confined within a tube housing the various cumbersome steps outlined above are necessary.